Defrost controls for heat pumps



Sept. 17, 1963 w. K. KYLE ETAL DEFROST CONTROLS FOR HEAT PUMPS FiledNOV. 20, 1962 Inveraiors: Wm 32111939, Bobea 15. Swaz by fli'inflnqy lI: u. o

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United States Patent M 3,103,793 DEFROST CONTROLS FOR HEAT PUMPS WilliamK. Kyle and Robert S. Stewart, Staunton, Va., as-

signors to Westinghouse Electric Corporation, East Pittsburgh, Pa., acorporation of Pennsylvania Filed Nov. 20, 1962, Ser. No. 238,902 2Claims. (Cl. 62140) This invention relates to heat pumps, and relatesmore particularly to controls for defrosting the outdoor coils ofmultiple system heat pumps having a common fan or common fans for movingoutdoor air over their outdoor coils.

An air conditioning system using a two system heat pump may be used forcooling indoor air in summer, and for heating indoor air in winter, onesystem being used for light loads, and both systems being used for heavyloads. The outdoor coils of the two systems may have a common fan orcommon fans for moving outdoor air over them. During indoor air heating,the indoor coils of the systems act as condenser coils, and theiroutdoor coils act as evaporator coils. Frost often forms on the outdoorcoils when they are acting as evaporator coils at low outdoortemperatures, and for proper operation they need to be defrosted. Thefrost may build up differently on the two outdoor coils so that afterdefrosting has started, one may finish defrosting before the other. Ourco-pending application, Serial No. 206,968, filed July 2, 1962,discloses controls for preventing the first system to finish defrostingfrom returning to normal, indoor air heating operation until the othersystem has finished defrosting. Our present invention is an improvementover the invention in said application in that fewer controls arerequired, resulting in a simpler and less expensive control system.

An object of this invention is to improve defrost controls for multiplesystem heat pumps.

Another object of this invention is to simplify and reduce the cost ofcontrols for defrosting the outdoor coils of multiple system heat pumps.

This invention will now be described with reference to the annexeddrawings, of which:

FIG. 1 is a diagrammatic view of a two system heat pump embodying thisinvention, the relays and the electrical wiring used being omitted, and

FIG. 2 is a circuit schematic showing the relays and wiring used, andshowing the switches which are open and which are closed when bothsystems are operating to heat indoor air.

Aligned, abutting, indoor coils and 11 have fans 12 and 13 respectively,driven by electric motors 14 and 15 respectively, for moving indoor airto be conditioned over the coils 10 and 11 and into the space to beserved. One end of the coil 10 is connected by tubing 16 to arefrigerant reversal valve RV1 which is connected by tubing 18 to oneend of outdoor coil 19, the other end of which is connected by capillarytube 20 serving as a two-way expansion device to the other end of thecoil 10. The valve RV1 is connected by tubing 26 to the interior ofelectric motor CM1 of refrigerant compressor C1, which interior isconnected to the suction side of the compressor C1 as is usual withhermetic compressors. The valve RV1 is connected by tubing 21 containinga high pressure cut-out HPCl, to the discharge side of the compressorC1. The valve RV1 is adjustable by solenoid SOLl to route refrigerantfrom the compressor C1 through the tubing 18 to the outdoor coil 19, andfrom the latter through the capillary tube 20 to the indoor coil 110when the latter is to act as an evaporator coil, and the outdoor coil 19is to act as a condenser coil, or to route refrigerant from thecompressor C1 through 3 ,10 3"793 Patented Sept. 17, 1963 2 the tubing16 to the indoor coil 10 and from the latter through the capillary tube20 to the outdoor coil 19 when the latter is to act as an evaporatorcoil, and the indoor coil 10 is to act as a condenser coil.

One end of the indoor coil 11 is connected by tubing 46 to a refrigerantreversal valve RV2 which is connected by tubing 28 to one end of outdoorcoil 29, the other end of which is connected by capillary tube 30serving as a two-way expansion device, to the other endv of the coil 11.The valve RV2 is connected by tubing 31 containing a high pressurecut-out HPC2 to the discharge side of hermetic compressor C2 which isdriven by electric motor CM2. The valve RV2 is connected by tubing '36to the interior of the motor CM2, which interior is connected .to thesuction side of the compressor C2. The valve RV2 is adjustable bysolenoid SOL2 to route refrigerant from the compressor C2 through thetubing 28 to the outdoor coil 29 and from the latter through thecapillary tube 3ll to the indoor coil 11 when the latter is to act as anevaporator coil, or to route refrigerant from the compressor C2 throughthe tubing 46 to the indoor coil 11 and from the latter through thecapillary tube 39 to the outdoor coil 29 when the latter is to act as anevaporator coil, and the indoor coil 11 is to act as a condenser coil.

The indoor coil 16, the outdoor coil 19, the com pressor C1 and theirassociated components form one system of the heat pump, and the indoorcoil [11, the outdoor coil 29, the compressor C2 and their associatedcomponents form the second system of the heat pump. The outdoor coils 19and 29 and the compressors C1 and C2 are supported within a cabinethaving outdoor air inlets 41 and 42 in its ends, and having an airoutlet 47 in its top. The coils 19 and 29 are slanted so that theydiverge towards the outlet 47, and within the space between the coilsbelow the outlet 47 is a fan OF driven by an electric motor OFM, whichdraws outdoor air through the inlets 41 and 42, passes this air over thecoils 19 and 29, and discharges this air through the outlet 47.

The compressor motor CM1 is connected in series with normally closedswitch MSIS of motor starter MSIl to AC. electric supply lines L1 andL2. The compressor motor CM2 is connected in series with normally closedswitch MS2S of motor starter MS2 to the supply lines. The motor starterM81 is connected in series with normally closed switch HPCIS of thecut-out HPCI to the supply lines. The motor starter M82 is connected inseries with normally closed switch HPC2S of the cut-out HPC2 to thesupply lines.

The pressure cut-outs HPCl and HPC2 are automatic resetting. Theyautomatically reclose their switches when the abnormal pressure that hasopened them decreases to normal.

The outdoor fan motor OFM is connected in series with normally closedswitch FRS of fan relay OFR to the supply lines L1 and L2.

The (fan relay OFR and the solenoids SOLl and SOL2 are connected inparallel, and are connected in series with a normally closed switch DRSIof defrost relay DR to the supply lines.

A defrost control DC is connected by tube 52 to the air between thecoils 19 and 29, and has a normally open switch DCS which closes whenthe air pressure between the coils 19 and 29 decreases as a result offrost having formed on either of the outdoor coils.

A defrost limit control DLl is connected to the interior of the coil 19so as to respond to the refrigerant pressure therein, and 'has anormally closed switch DLlS. A similar defrost limit control DL2 isconnected to the interior of the coil 29 so as to respond to therefrigerant pressure therein, and has a normally closed switch DL2S. Theswitches DLlS and DL2S open when the pressures within the coils 19 and29 respectively, increase to normal pressures of about 220-250 p.s.i.when the frost has melted from them when they are operating as condensercoils. When the coils 19 and 29 are operating as evaporator coils, thepressures within them are insufiicient to open the switches DL1S andDLZS, such pressures being, for example, at B, only 16 psi.

A normally deenergized defrost relay DR has a normally closed switchDRSI and a normally open switch DRS2. The relay DR is connected inseries with the switches DLlS and DLZS which are connected in parallelwith each other, and the switches DCS and DRSZ connected in parallelwith each other, to the supply lines L1 and L2.

Operation In operation, it is assumed that an associated indoorthermostat which is not shown, has turned both systems of the heat pumpon, and that the outdoor coils are operating as evaporator coils beforesubstantial frost has formed on them. When substantial frost has formedon the coils 19 and 29, the resulting air pressure drop through themwill cause the switch DCS to close and to energize through the normallyclosed switches DL1S and DL2S, the defrost relay DR which opens itsswitch DRSI and closes its switch DRSZ. The closing of the switch DRSZestablishes a holding circuit for maintaining the relay DR energizeduntil both switches DLlS and DLZS open. The opening of the switch DRSIdeenergizes the relay CPR and the solenoids SOLl and SOLZ. The relay OFRopens its switch FRS which stops the fan motor OFM. 'Ihe solenoids SOLIand SOLZ adjust the reversal valves -RV1 and RV2 respectively, tooperate the indoor coils 10 and 11 respectively, as evaporator coils,and the outdoor coils 19 and 29 respectively, as condenser coils. Theheat from the outdoor coils melts the frost thereon.

Assume that the coil 19 completes its defrosting first so that thepressure within it increases and opens the switch DLlS. The defrostrelay remains energized through the still closed switches DLZS and DRSZso that the defrosting continues. The compressor motor CMl remains onuntil the rise in refrigerant pressure operates the cut-out HPCI to openits switch HPClS which deenergizes the motor starter M81 and stops themotor (3M1.

When the outdoor coil 29 completes its defrosting, the pressure withinit increases and opens the switch DLZS, deenergizing the defrost relayDR. The latter then reopens its switch DRS2 and recloses its switchDRSl. The closed switch DRSl reenergizes the solenoids SOLl and SOLZ andthe fan relay OFR. The solenoids SOL1 and SOLZ return the reversalvalves RVl and RVZ respectively to indoor air heating positions with theoutdoor air coils 19 and 29 again operating as evaporators, and theindoor coils 10 and 11 again operating as condensers. The fan relay OFRrecloses its switch FRS, restarting the outdoor fan motor OFM. Thereduction in refrigerant pressure permits the cut-out HPCI to recloseits switch HPCIS, restarting the compressor motor CMl. The two systemsof the heat pump arenow back in normal indoor air heating operation.

What is claimed is:

1. An air conditioning system comprising a first refrigerant compressor,a first indoor coil, a first outdoor coil, means including a firstreversal valve connecting said compressor to said coils, a firstsolenoid for adjusting said valve to operate said outdoor coil as anevaporator coil or as a condenser coil, a second refrigerant compressor,a second indoor coil, a second outdoor coil, means including a secondreversal valve for connecting said second compressor to said secondcoils, a second solenoid for adjusting said second valve to operate asan evaporator coil or as a condenser coil, a common fan for movingoutdoor air over said outdoor coils, an electric motor for driving saidfan, a defrost control responsive to air pressure drop across saidoutdoor coils, said control having a normally open switch which closeswhen there is a predetermined pressure drop across said outdoor coils, afirst limit control responsive to refrigerant pressure within said firstoutdoor coil, said limit control having a normally closed switch whichopens when there is a predetermined pressure within said first outdoorcoil, a second limit control responsive to refrigerant pressure withinsaid second outdoor coil, said second limit control having a normallyclosed switch which opens when there is a predetermined pressure Withinsaid second outdoor coil, said switches of said limit controls beingconnected in parallel, a normally deencrgized defrost relay having anormally open switch connected in parallel with said switch of saiddefrost control and having a normal'ly closed switch, electric supplyconnections, means including said switch of said defrost control andsaid switches of said limit controls for connecting said relay to saidconnections, and means including said normally closed switch of saidrelay for connecting said solenoids and said motor to said connections.

2. An air conditioning system comprising a first refrigerant compressor,a first electric motor for driving said compressor, a first indoor coil,a first outdoor coil, means including a first reversal valve forconnecting said compressor to said coils, a first solenoid for adjustingsaid valve to operate said outdoor coil as an evaporator coil or as acondenser coil, a second refrigerant compressor, a second electric motorfor driving said second compressor, a second indoor coil, a secondoutdoor coil, means including a second reversal valve for connectingsaid second compressor to said second coils, a second solenoid foradjusting said second valve to operate said second outdoor coil as anevaporator or as a condenser coil, a common fan for moving outdoor airover said outdoor coils, a third electric motor for driving said fan, adefrost control responsive to air pressure drop across said outdoorcoils, said control having a normally open switch which closes whenthere is a predetermined air pressure drop across said outdoor coils, afirst limit control responsive to refrigerant pressure within said firstoutdoor coil, said limit control having a normally closed switch whichopens when there is a predetermined pressure within said first outdoorcoil, a second limit control responsive to refrigerant pressure withinsaid second outdoor coil, said second limit control having a normallyclosed switch which opens when there is a predetermined pressure withinsaid second outdoor coil, said switches of said limit controls beingconnected in parallel, a normally deenergized defrost relay having anormally open switch connected in parallel with said switch of saiddefrost control, said relay having a normally closed switch, electricsupply connections, means including said switch of said defrost controland said switches of said limit controls for connecting said relay tosaid connections, means including said closed switch of said relay forconnecting said solenoids and said third motor to said connections, afirst pressure cutout responsive to refrigerant pressure from said firstcompressor, said cut-out having a normally closed switch, meansincluding said switch of said cut-out for connecting said first motor tosaid connections, a second cut-out responsive to refrigerant pressurefrom said second compressor, said second cut-out having a normallyclosed switch, and means including said switch of said second cut-outfor connecting said second motor to said connections, said switches ofsaid cut-outs opening when the pressures from said compressors areabnormal and automatically reclosing when the pressures from saidcompressors return to normal.

Gibson Nov. 12, 1940 Keller Oct. 17, 1961

1. AN AIR CONDITIONING SYSTEM COMPRISING A FIRST REFRIGERANT COMPRESSOR, A FIRST INDOOR COIL, A FIRST OUTDOOR COIL, MEANS INCLUDING A FIRST REVERSAL VALVE CONNECTING SAID COMPRESSOR TO SAID COILS, A FIRST SOLENOID FOR ADJUSTING SAID VALVE TO OPERATE SAID OUTDOOR COIL AS AN EVAPORATOR COIL OR AS A CONDENSER COIL, A SECOND REFRIGERANT COMPRESSOR, A SECOND INDOOR COIL, A SECOND OUTDOOR COIL, MEANS INCLUDING A SECOND REVERSAL VALVE FOR CONNECTING SAID SECOND COMPRESSOR TO SAID SECOND COILS, A SECOND SOLENOID FOR ADJUSTING SAID SECOND VALVE TO OPERATE AS AN EVAPORATOR COIL OR AS A CONDENSER COIL, A COMMON FAN FOR MOVING OUTDOOR AIR OVER SAID OUTDOOR COILS, AN ELECTRIC MOTOR FOR DRIVING SAID FAN, A DEFROST CONTROL RESPONSIVE TO AIR PRESSURE DROP ACROSS SAID OUTDOOR COILS, SAID CONTROL HAVING A NORMALLY OPEN SWITCH WHICH CLOSES WHEN THERE IS A PREDETERMINED PRESSURE DROP ACROSS SAID OUTDOOR COILS, A FIRST LIMIT CONTROL RESPONSIVE TO REFRIGERANT PRESSURE WITHIN SAID FIRST OUTDOOR COIL, SAID LIMIT CONTROL HAVING A NORMALLY CLOSED SWITCH WHICH OPENS WHEN THERE IS A PREDETERMINED PRESSURE WITHIN SAID FIRST OUTDOOR COIL, A SECOND LIMIT CONTROL RESPONSIVE TO REFRIGERANT PRESSURE WITHIN SAID SECOND OUTDOOR COIL, SAID SECOND LIMIT CONTROL HAVING A NORMALLY CLOSED SWITCH WHICH OPENS WHEN THERE IS A PREDETERMINED PRESSURE WITHIN SAID 